Big E is useful to an O-Gauger IF you've completed a layout to the point where you only really need scenery materials. Otherwise the overwhelming majority of locomotives and rolling stock is HO or N. Virtually all of the dedicated O Gauge dealers I found in one side of a single exhibit hall, with maybe a couple of outliers in the other halls..
York inverts this in favor of the O-Gauger (you can find scenery stuff and HO, but it's mostly confined to one side of one hall).
---PCJ